The invention generally is related to a marker system for locating positions within the blood vessels of a patient so that diagnosis can be made at or between the positions or so that treatment can be rendered there. More particularly, the invention is a marker system with one or more indicators that can be visualized under X-ray imaging, for example radiography or fluoroscopy, while treatment or diagnosis is undertaken using catheters or other instruments inserted into the vasculature, such as when an intraluminal graft is being implanted, to guide the placement of the catheter or instruments.
Catheters long have been used for the purpose of diagnosing anomalous conditions in the vasculature or for rendering treatment therein. For example, catheters have been used to deploy grafts, to remove occlusions and to expand areas affected by arteriosclerosis. Procedures employing catheters are attractive because use of catheters avoids more surgically invasive procedures, minimizing the risks to the patient.
The effectiveness of any catheterization procedure heavily depends on the ability of the clinician to accurately locate the area of the vasculature at which a diagnosis is to be made or treatment is to be rendered. Various systems and methods have been proposed to facilitate this location process. Most involve fluoroscopic visualization of the vasculature using a radiopaque dye with a catheter equipped with radiopaque tags, which tags also can be detected by radiographic means. Because radiopaque dye injected into the blood vessels quickly is dispersed through action of the circulatory system, the clinician heretofore has had to rely on the clinician's recollected image of the almost instantaneous visualization of the blood vessels in order to pinpoint the site at which diagnosis or treatment is to take place.
Recently, computerized digital substraction technology, colloquially known as "roadmapping," has been developed to aid the clinician's memory. This technique effectively takes a picture of the fluoroscopic image of the blood vessels when the vessels are illuminated by the radiopaque dye and uses a computer to digitize the image. The digitized image then can be superimposed over an analog, "real time" image that tracks the progress of a radiopaque-tipped catheter through the vasculature. This technique greatly reduces the clinician's need to rely on the clinician's memory to target the approximate site at which diagnosis or treatment is to take place. However, the technique does not allow the clinician to precisely mark where within a particular vessel a procedure is to be performed.
Catheter systems are especially well-suited for deploying arterial grafts to an area within the abdominal aorta which is affected by an aneurysm, in order to relieve pressure on the vessel walls. An aneurysm is a bulged area of a vessel that is caused by genetic defects or, more commonly, by disease that might or might not be a result of genetics such as arteriosclerosis. If the pressure at the aneurysm is not relieved by some means, the vessel might rupture. Grafts often are placed at the location of aneurysms to create an artificial passageway for blood flow, so the blood pressure is sustained by the graft and not the wall of the vessel. A frequent site of occurrence of abdominal aortic aneurysms is the portion of the aorta just caudal to the branch point of the renal arteries. In a typical procedure to locate an aneurysm, the clinician can identify the site at which a graft is to be deployed by using fluoroscopy or other radiography techniques. This identification step can be accomplished with the technique of X-ray film subtraction or, more modernly, with the technique of Digital Subtraction Angiography (DSA).
In DSA, a catheter is inserted into a blood vessel in the area of interest and a baseline or pre-injection image is captured using an X-ray source, an X-ray image intensifier, a fluoroscopic television, and a computer. The image is digitized and then stored by the computer. Then a bolus of dye containing iodine or another substance that readily can be visualized under fluoroscopy is injected through the catheter and another radiographic image or rapid series of images is captured, digitized and stored while the dye is present in the vessels of interest and before it has dissipated through the bloodstream. The computer subtracts the pre-injection image from the images acquired just after injection, performs some enhancement operations, and produces a static digital image of the blood vessels. A more time consuming but sometimes more accurate process of film subtraction involves superimposing a pre-injection X-ray film on a post-injection X-ray film to produce a static image.
After the static image has been obtained, the catheter used in the procedure to obtain it might be removed in order to insert a second catheter bearing the intraluminal graft to be implanted. Alternatively, the in-place catheter already may be carrying the graft. The catheter used to carry the graft to the implantation site usually has a distal end configured to allow the catheter to negotiate the anatomy of the vascular system. The graft then can be delivered by anchoring the ends of the graft to the vessel wall, such as with hooks attached to the graft. Thus, when the catheter is removed, the graft remains in place, and provides a passageway for the blood to move through without applying any pressure to the aneurysm.
In order for the graft to effectively perform its pressure relieving function, it is critical that the graft be implanted so that it extends along the full length of the aneurysm. Identifying where the anchoring systems should be placed is difficult when the clinician only has radiographic subtraction techniques upon which to rely. Such techniques merely guide the clinician to the approximate area of the vasculature in which the aneurysm appears. The techniques do not allow identification of where the proximal and distal ends of the graft should be affixed.
What is needed and has heretofore been unavailable then, is a marker system that can be used with existing radiographic techniques for locating particular positions within the blood vessels of a patient, to allow a clinician to accurately place a graft at the site of an aneurysm, or to render other treatment or perform a diagnosis at an affected site in the vasculature. The present invention fulfills this need.